This invention relates to a new process for the preparation of diacetone acrylamide (also referred to hereinafter as DIAC), also known as N-(1,1-dimethyl-3-oxobutyl)acrylamide, which is represented by formula (I). ##STR1##
Applicant is not aware of any prior art reference which, in his judgment as one skilled in the art of preparing diacetone acrylamide, would anticipate or render obvious the process of the instant invention; however, for the purpose of fully developing the background of the invention and establishing the state of the requisite art, the following references are set forth.
In U.S. Pat. No. 3,649,688, an improved method is disclosed for preparing DIAC by reacting acrylonitrile with diacetone alcohol in the presence of sulfuric acid, the improvement comprising preparing a mixture of acrylonitrile and sulfuric acid, said sulfuric acid being at least 93% concentration, and the molar ratio of sulfuric acid to acrylonitrile being at least 1.6 to 1, introducing the diacetone alcohol into said mix at a temperature below 30.degree. C. and maintaining said temperature during the reaction of the alcohol with the acrylonitrile, and recovering the DIAC from the reaction mixture. However, the product obtained is yellow-colored and contains about 5-10% by weight of acrylamide by-product.
In U.S. Pat. No. 3,542,867, an improved method is disclosed for preparing diacetone acrylamide by reacting diacetone alcohol, or mesityl oxide, or at least 2 moles of acetone in the presence of acrylonitrile and sulfuric acid, the improvement consisting of diluting the reaction mixture with water to a sulfuric acid content of 25-80% by weight, extracting the DIAC from the acidic reaction mixture with a water-immiscible organic solvent and recovering the DIAC from the extract.
In U.S. Pat. No. 3,542,875, an improved method is disclosed for preparing DIAC by reacting one mole of acrylonitrile with at least one mole of diacetone alcohol or mesityl oxide, or with at least two moles of acetone, in the presence of at least one mole of sulfuric acid, neutralizing the reaction mixture by addition of alkali to a pH at least above 7.5 and subsequently extracting with a water-immiscible organic solvent and recovering DIAC therefrom, the improvement consisting of heating the organic solution of DIAC at 50.degree.-100.degree. C. with aqueous alkali and recovering DIAC from the organic solution.
The DIAC produced by the process of the present invention has advantages over that produced by the processes of U.S. Pat. Nos. 3,542,867 and 3,542,875 in that it requires no further purification after isolation. The product obtained is substantially free of colored and polymeric by-products.
In U.S. Pat. No. 3,277,056, a series of equations is disclosed to illustrate the preparation of diacetone acrylamide by reacting diacetone alcohol and acrylonitrile in the presence of sulfuric acid. A hypothetical intermediate in this reaction is assigned formula (II) ##STR2## with the understanding that the formula is only illustrative. However, no intermediate such as (II) is actually isolated.
In general, the prior art teaches the preparation of DIAC by reacting acrylonitrile and 4-hydroxy-4-methyl-2-pentanone in the presence of at least 93% sulfuric acid, the mole ratios of said sulfuric acid and acrylonitrile to said 4-hydroxy-4-methyl-2-pentanone being about 1-2 and 1-1.5 moles, respectively, at a temperature below 15.degree. C., allowing the reaction mixture to warm up to ambient to moderately elevated temperatures to complete the reaction, cooling the reaction mixture, contacting the reaction mixture with water and a water-immiscible organic solvent, neutralizing the aqueous phase with an alkalizing agent, separating the organic phase, stripping the organic phase of volatile materials, and recovering N-(1,1-dimethyl-3-oxobutyl)acrylamide therefrom.
DIAC is useful in photographic films, adhesives, as a reactive cross-linking monomer in unsaturated polyester resins, as a stabilizer in paper and glass reinforced prepregs, and as an additive in hydrocarbon oils. For a description of how to use as an oil additive, see for example, U.S. Pat. No. 3,227,056, Example 18, which is incorporated herein by reference.
In order to obtain DIAC of acceptable color and purity for use in photographic films, it has been generally necessary either to distill or recrystallize the crude product.
There is a need, therefore, for a process that will give high yields of essentially colorless DIAC, having a melting point above 54.degree. C., which does not have to be purified by subsequent recrystallization or distillation.